The project would modernize Concourse D — home to United, Delta, Jet Blue and US Airways — and create a secure connection to the international gates on Concourse E at Baltimore-Washington International Thurgood Marshall Airport. The new configuration would allow two Concourse D gates to be used for overseas flights.

The preliminary schedule calls for the design to be ready by fall 2014 and construction to be completed in fall 2016.

BWI will ask the Board of Public Works on July 24 to approve money to hire a designer and construction management company to draft blueprints.

“This development plan will support hundreds of jobs for Marylanders and increase travel, trade and business development in our state,” Gov. Martin O’Malley said in a statement. “Together, we are expanding opportunities for growth at BWI Marshall as a convenient, efficient airport for travelers throughout the region.”

The project will be paid for with $100 million from BWI’s passenger facility charges collected on each airline ticket and $25 million from the state’s Transportation Infrastructure and Investment Act of 2013.

The airport’s executive director, Paul Wiedefeld, who flew to Dallas on Thursday to brief Southwest officials on the proposal, characterized their response as “very pleased.”

“This is clearly building the house that is the next chapter in our relationship,” Hawkins said. “BWI is clearly hedging on low fares, high customer service and low fees on international routes, and that’s what Southwest is all about.”

While Hawkins acknowledged Southwest’s international interest, the airline has not laid out specific plans. Southwest has told the airport it intends to start flying international routes perhaps as early as 2015, Wiedefeld said.

BWI’s proposal comes as the region’s busiest airport puts the finishing touches on a $100 million terminal expansion for domestic flights, continues a $356 million runway rehabilitation program and begins planning with the FAA for a new 228-foot air traffic control tower.

The FAA wants to replace the three-decade-old existing tower over Concourse C with a taller tower able to observe the entire airport. A new tower, at a cost of at least $26 million, could be integrated into another construction project at the airport.

Last year, BWI handled 22.7 million passengers, making it the nation’s 22nd-busiest airport. Its aggressive expansion program, which included a daily parking garage and off-site rental car facility, is tied to the continuing growth of Southwest, the nation’s No. 3 airline and responsible for 70 percent of BWI’s commercial traffic.

Southwest signaled its intent to enter the global market when it purchased AirTran for $1.4 billion in 2010 and gained that airline’s routes to the Caribbean and Latin America. It has upgraded its ticketing system and begun purchasing longer-range jets.

BWI has struggled to retain international flights over the past two decades as the airport lost much of its business to Dulles, outside Washington, and to Philadelphia International Airport. In the late 1990s, then-USAir stopped service from BWI to South America and the Caribbean. Icelandic Airlines left in 1999. In 2004, Aer Lingus ended service to Ireland that began in 2000. Mexicana pulled out in 2007 after two years. Icelandair ended 17 years of flights from BWI to Reykjavik in 2007.

But international traffic is on the rise at BWI, with passenger counts up nearly 21 percent in 2012 over the prior year.

Today, BWI’s Concourse E is served by the military’s Air Mobility Command, British Airways, Condor, Air Canada and charters. With Southwest poised to enter the international market, Wiedefeld said, it was clear that something had to change.

“During peak periods — 6 p.m. to 9 p.m. — we use all six gates,” he said. “We continue to talk to other carriers, but we can’t pursue other opportunities. I don’t want to be sitting here without any gates to offer them, and you don’t build these things overnight.”

But the expansion plan is more than a ticket to an increase in international flights.

The Concourse D security checkpoint, a claustrophobic holding area that forces waiting passengers to snake along a narrow, windowless corridor, will be replaced by an arrangement similar to the checkpoints and connectors at concourses A, B and C.

“Clearly, now that the B-C connector is open, we know the constraints of [Concourse] D and we have to fix that,” Wiedefeld said.

The 10-lane checkpoint to serve both Concourse D and international passengers will open to a sweeping boulevard with floor-to-ceiling windows overlooking the runways and taxiways. The hallway linking the two branches of the concourse to the terminal will be widened, and a secure walkway will allow passengers making international connections to proceed without being rescreened.

Wiedefeld said that by designating two of the Concourse D gates for both domestic and international flights, BWI will gain capacity without added construction. He said that if an airline expresses interest in leasing international space before construction is completed, the two D gates could be opened early.